A magneto rotor is known having a substantially cylindrical and cup-shaped drum having at one end a base plate formed with a central axial hole in which a hub is received and formed off set from this hole with a plurality of ventilating apertures. Inside the drum and angularly spaced about its cylindrical interior surface is a plurality of magnetic inductors each formed by a permanent magnet and a pole piece of high magnetic permeability.
In use the rotor described above is spun at high speed about its axis so that current can be generated in stationary coils juxtaposed with the inductors inside the drum. Such an arrangement is typically used on small combustion engines, as for instance in two-wheel vehicles for generating the electricity that powers the ignition and that operates the head and running lights of the vehicle.
Such an arrangement is subjected to considerable vibration and miscellaneous shocks, so that the inductors constituted by the magnets and the pole pieces must be extremely securely fixed inside the drum. Should one of the inductors come loose the inevitable result is almost immediate stoppage of the engine and destruction of the magneto assembly.
As the magnets are normally formed of a ceramic-like material such as ferrite it is extremely difficult to shape them, or to bore them out so as to make their mounting an easy task. Similarly, the very hard pole pieces, normally formed of steel, cannot be machined to exact specifications either without considerably increasing the cost of the magneto rotor.
It has been suggested in French Pat. No. 1,125,118 to hold the inductors in place by means of a cast aluminum cage which is adhesively secured in place with the inductors. Such an arrangement is completely satisfactory with relatively small magnetos, normally having less than four poles. However, it has been found to be of little use in larger assemblies where, for ventilation, it is necessary to separate the inductors considerably, so that the aluminum holding cage must be formed with such large spaces for ventilation that it has no strength and cannot serve its intended function.